The present invention relates to curable coating compositions, and more particularly to curable coating compositions comprising as a vehicle component a nitrogen-containing condensation resin having nitrogen atoms in its main skeleton.
Alkyd resin coating compositions are in wide use which comprise as a vehicle component an alkyd resin prepared from a polybasic acid and a polyhydric alcohol (further in combination with a fatty acid for modifying the resin when desired) by subjecting these compounds to a condensation reaction. These compositions are available at a low cost and excellent in coating operation efficiency, adhesion to substrates and bulky appearance (especially when finished in a solid color).
With rapid technical innovation, improved properties are inevitably required of coating compositions at present.
Alkyd resin coating compositions are still low in pigment dispersibility and pigment dispersion stability and therefore have the drawbacks that the coating obtained is inferior in gloss, distinctness-of-image gloss and finished appearance and also in properties such as adhesion, corrosion resistance, chemical resistance and mechanical characteristics. It has been required to remedy these drawbacks.
We have already proposed a curable coating composition comprising as a vehicle component a nitrogen-containing alkyd resin which has nitrogen atoms introduced into its main skeleton by using a alkalonol amine having at least two hydroxyl groups in the molecule as a portion or the whole of the polyhydric alcohol serving as one of the components of the alkyd resin (Japanese unexamined publication No.28562/1986). Said coating composition can somewhat attain the improvement in the above drawbacks of the alkyd resin coating compositions, but remains to be improved in the properties of coatings such as corrosion resistance, mechanical characteristics, etc.
In recent years, on the other hand, cationic electrodeposition coating compositions have been generally used in place of anionic electrodeposition coating compositions because these cationic compositions form cured coatings having substantially excellent corrosion resistance due to the mechanism of electrodeposition and the basic properties of their resin component. Among cationic coating compositions, widely used are those comprising as the base resin an epoxy resin having cationic groups introduced therein since the coating formed has high corrosion resistance. However, these compositions have the problem of being costly and having low weather resistance. Accordingly, it has been desired to provide cationic electrodeposition coating compositions of the water-soluble alkyd resin type which are less costly, whereas alkyd resin compositions generally have the foregoing drawbacks. Further cationic electro-deposition coating compositions which comprise water-soluble alkyd resin such as amino alkyd resin having hydroxyl and like cationic groups and curing agent are low in corrosion resistance and in the chemical and mechanical properties of coatings. Thus, cationic electrodeposition coating compositions of the alkyd resin type which are free of such drawbacks still remain to be provided.